Field of the invention
The present invention relates to a device for simultaneous automatic controlling or checking the distance between cathodes and the second grid of a trichromatic cathode tube gun.
Determination of the distance between the emitting surface of each of the three cathodes and the first grid G1 of a trichromatic cathode tube gun is very important during the manufacture of a cathode tube electron gun in order to ensure, in large-scale manufacture, the constancy of the focussing qualities of the gun grids. The measuring of this distance cannot be directly performed due to the form and the dimensions of the gun.
According to the current state of the art, this distance is indirectly determined by measuring the distance between each cathode and the second grid G2, the access to this second grid being possible through the other grids, the distance between G1 and G2 being estimated. However, the devices normally used for this purpose are bulky, and thus do not allow simultaneous measuring for the three cathodes, and their carrying out in an automated measuring method does not allow to guarantee against any risks of shock on the cathode or the grid G2.
The aim of the present invention is to provide a device allowing the simultaneous automatic checking of the distance of each of the three cathodes to the grid G2, such a device ensuring a very smooth conveyance of the measuring elements in contact with the cathodes and of G2, while performing a very rapid and accurate control.